Why Evolution Is True

Jerry A. Coyne from the University of Chicago is a distinguished biologist of Speciation fame and a well-known figure in the intelligent design vs. evolution debate. He for some reason felt obliged to lay out the evidence for evolution, but unlike the one mentioned above, which is a highly technical textbook (co-authored with H. Allen Orr) and an embarrassingly difficult read even for professionals, Why Evolution Is True is a delightful book designed for the average reader.

Isn’t this so-called ID-evolution debate already settled? Apparently not. Not in America, at any rate. While it’s not really an issue in Europe, a great number of people in the United States flatly reject evolution and literally interpret the Bible as the ultimate truth.

But here’s the thing: the evidence for evolution is overwhelming. It’s there for all to see. Paleontology, geology, plate tectonics, biogeography, comparative anatomy, genetics, molecular biology – all these disciplines have their share to add to the ever-growing pile of evidence. You have to be blind or just plain stupid to deny it.

At any rate, Dr. Coyne makes his attempt to impart this intelligence to the lay people. After explaining in the first chapter what evolution is, in the following chapters he makes his case clearly with numerous examples from the above disciplines. Chapter 2 deals with fossils, how paleontologists work, radioactive dating methods, prominent transitional fossils like Tiktaalik (fish to amphibian), Archaeopteryx (reptile to bird), Indohyus (an artiodactyl ancestor of whales). This is really just an excerpt. There are a lot more.

Chapter 3 happens to contain my favourite example, one from ontogenesis. Not the easiest to understand, but I hadn’t known about it before. I recommend medical students pop this to their anatomy teacher: why the heck does our left recurrent pharyngeal nerve go all the way down to the heart and come back only to innervate the larynx?

The answer lies in ontogenesis and common ancestry:

One of nature’s worst designs is shown by the recurrent laryngeal nerve of mammals. Running from the brain to the larynx, this nerve helps us speak and swallow. The curious thing is that it is much longer than it needs to be. Rather than taking a direct route from the brain to the larynx, a distance of about a foot in humans, the nerve runs down into our chest, loops around the aorta and a ligament derived from an artery, and then travels back up to connect to the larynx. It winds up being three feet long. In giraffes the nerve takes a similar path, but one that runs all the way down that long neck and back up again: a distance fifteen feet longer than the direct route! When I first heard about this strange nerve, I had trouble believing it. Wanting to see for myself, I mustered up my courage to make a trip to the human anatomy lab and inspect my first corpse. An obliging professor showed me the nerve, tracing its course with a pencil down the torso and back up to the throat.
This circuitous path of the recurrent laryngeal nerve is not only poor design, but might even be maladaptive. That extra length makes it more prone to injury. It can, for example, be damaged by a blow to the chest, making it hard to talk or swallow. But the pathway makes sense when we understand how the recurrent laryngeal nerve evolved. Like the mammalian aorta itself, it descends from those branchial arches of our fishlike ancestors. In the early fishlike embryos of all vertebrates, the nerve runs from top to bottom alongside the blood vessel of the sixth branchial arch; it is a branch of the larger vagus nerve that travels along the back from the brain. And in adult fish, the nerve remains in that position, connecting the brain to the gills and helping them pump water.
During our evolution, the blood vessel from the fifth arch disappeared, and the vessels from the fourth and sixth arches moved downward into the future torso so that they could become the aorta and a ligament connecting the aorta to the pulmonary artery. But the laryngeal nerve, still behind the sixth arch, had to remain connected to the embryonic structures that become the larynx, structures that remained near the brain. As the future aorta evolved backward toward the heart, the laryngeal nerve was forced to evolve backward along with it. It would have been more efficient for the nerve to detour around the aorta, breaking and then re-forming itself on a more direct course, but natural selection couldn’t manage that, for severing and rejoining a nerve is a step that reduces fitness. To keep up with the backward evolution of the aorta, the laryngeal nerve had to become long and recurrent. And that evolutionary path is recapitulated during development, since as embryos we begin with the ancestral fishlike pattern of nerves and blood vessels. In the end, we’re left with bad design.

The following chapters deal with the geography of life, how animals came to live in the separate continents, island biogeography, bees killing giant hornets by heating them up to 80 degrees centigrade, evolution in the test tube, drug resistance, a whole chapter on sexual selection, speciation (the process of distinct species formation), population genetics, human evolution (including Homo floresiensis, the hobbit), etc.

All in all, a profoundly satisfying read, a rare gem in the market of popular science books. Last words:

We are the one creature to whom natural selection has bequeathed a brain complex enough to comprehend the laws that govern the universe. And we should be proud that we are the only species that has figured out how we came to be.

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32 Comments

This might seem like bad design or evidence for evolution but let me show you why this is not the case. Biologists believe in evolution because they think like biologists and not like engineers.

The left recurrent laryngeal nerve branches of the vagus nerve and links to the larynx. This is its only purpose. But in order for it to branch of the vagus nerve it would need a marker, from an engineering perspective, to decide when to branch off. Imagine you are driving along a motorway, how do you know when to turn off? You use markers like signposts, buildings or natural landmarks right. In the developing fetus there are very few landmarks to begin with and if you have ever seen a tiny fetus in a scan you will know that virtually all that you can see is a tiny beating heart. The heart, lungs and brain are the first organs to develop and can be used as the key markers for further development.

Furthermore, DNA shows that each of us is unique with jumping sequences of genetic information allowing for great diversity among individuals. If the branching point had been a random point on the vagus nerve, perhaps too much diversity would be permitted. Some people would have very long left recurrent laryngeal nerves while others would have very short ones. Alternatively, using a fixed point along the vagus nerve would also be no good as we all differ in size. By using the aorta as a marker and looping around it, the great designer might be preventing too much diversity.

Imagine a piece of software code where a calculation needs to be carried out. More often than not the calculation will not be done at the point that it is needed but a call is made to a function which carries out the calculation. This might seem inefficient on the face of it but software engineers will tell you that there are many good reasons for doing it this way. Similarly from an engineering perspective the long circuitous path of this nerve makes perfect sense but to a biologist this might seem illogical. This inefficient route the nerve takes actually proves design rather than evolution.

Adolfo Rivero said,

Some got eyes (which are also badly designed) but can not see. Blind by religious views these people can not understand the fascinating world we live in. A world were life evolved for millions of years. For those who work with genomes it is more than clear that we, and all other organisms, evolved as there are not only similarities in genes but in gene clusters, regulatory elements, etc. Sad to see some still trying to believe the the World is flat or it is the centre of the universe.

Anonymous said,

Richard C said,

So your argument is that God engineered us but couldn’t figure out how to run a direct route between the brain and neck?

The thyroid is also in your neck and its nerve runs a direct route. Guess it is possible after all.

In fact, thinking like a biologist or engineer is at the heart of this problem. Biology explains the length of it very well: it evolved from a known nerve in fish that runs a similar route, before the descending of the heart made the route laborious. It’s engineering that can’t explain it. Engineering would run a direct “wire” there. That direct nerve would preferred by engineering but impossible in biology because of the constraints provided by the theory evolution.

Michael said,

“World of Science” — I assume from your post that your handle has an ironic intent, eh?. The modern understanding of evolution does not, as you say, propose that humans are “the pinnacle of the evolutionary process.” Many religions make such a claim but biologists do not. In fact, humans are the products of a long, contingent process and remain vulnerable to the ever-present danger of extinction as do all other species. Should humans pass into oblivion as have virtually all creatures who came before us, it’s highly uncertain, and perhaps extremely unlikely that a being with a similar level of intelligence and creativity would evolve to replace us in our “niche” of world domination. I’ve read Jerry Coyne’s book and found it beautifully written and exceptionally clear, with many fascinating details illustrating how much we actually know with certainty about our origins and our commonality with other organisms. As Sam Harris has said, it’s counterintuitive that we share a common ancestor with a “house fly and a banana” but it’s true, science denialists such as yourself and the “engineer” who posted before you notwithstanding.

Steve said,

Your argument makes zero sense. Yes, when we pass a place we may need to mark our point to know where to go. That’s because we have cognition, vision, memory, and consciousness. A nerve that is growing, however, doesn’t have this (which is logically quite obvious, but apparently people arguing for creation don’t usually think logically… they just find some blind metaphor and vaguely connect it to prove whatever point they’re trying to prove.) Nerves follow a blueprint… a blueprint that has been developing for thousands of years. If this extra length in the cord is to “prevent diversity” (lol) then why does every animal have it (including *GASP* apes and monkeys).

Alan Gateway said,

I have had the chance to investigate the left recurrent laryngeal nerve in more depth since my previously submitted comments. I now wonder why we have singled out the left nerve. The right laryngeal nerve is also recurrent and also loops around an artery. There is nothing exceptional or odd about the left nerve. Infact the same arguments can be applied to both nerves although the recurrent nature is more pronounced in the left nerve than the right as the left is longer. These nerves are essential as vocal chords and for the act of swallowing.

If we went along with some of the evolutionary commentators above and rearranged these nerves so that they connected directly I doubt very much whether we would be able to speak or make the rich variety of vocal sounds that we can. We might even have great difficulty in swallowing the great variety of objects and foods that we can. These nerves have to be long and they have to be stretched. Looping around the arteries enables this stretching to occur during the growth phase in a natural way. The great designer has shown once again that his intellect is far superior to ours.

Steve said,

Again, your comment doesn’t really make any logical sense to someone who understands the physiological nature of nerves and how they function.

“These nerves are essential as vocal chords”
Incorrect. They connect to muscles and control contraction/relaxation; they are not directly related in the production of sound.

“These nerves have to be long and they have to be stretched.”
As told by all other nerve connections in our body, the length only serves to reach from one place to another (and the longer the connection, the slower the signal reaches its target). These nerves aren’t “stretched,” they are elongated. It’s not like they were x length and then “stretched” to reach a certain point. It’s actually kind of laughable that someone thinks this? It doesn’t make any logical sense. Physiologically, stretching a nerve is bad; they are supposed to be densely packed together to increase electrical conductivity.

“The great designer has shown once again that his intellect is far superior to ours.”
If his intellect is “far superior” then why were you able to figure it out so easily? Because your explanation makes no sense.

Please, get a Ph.D. or at least learn more about human physiology before you make these false rationalizations.

I do have to commend you for trying, though. Most would just say “God made it and I do not question it,” although you are somewhat failing in the “questioning” bit, since you’re just grasping straws trying to prove “God” right. Either way, good job sort of.

Alan Gateway said,

I disagree that the nerves are elongated. The nerve loops tightly around the aortic arch providing a degree of tension that is required for vocalisation. The nerve connects to the vocal chords which are responsible for providing the vibrations for sound production. The default setting here is one of tension within the vocal chords (provided for by the laryngeal nerves) which allows a simple signal from the brain to induce vibrations within the chords for speech. A lack of tension in the nerve as evidenced by 0.1% of the population who have a non recurrent laryngeal nerve results in poorer abilities to vocalise and the nerves and chords being overworked and tiring easily. Ofcourse this doesn’t mean that they cannot speak. Infact, the fact that they can speak is incorrectly used as evidence that the circuitous path of the nerve is unnecessary.

Roberto Aguirre Maturana said,

I’ve read some information indicating that larynx innervation isn’t the only function of recurrent laryngeal nerve. It seems to innervate also the esophagus, the trachea and the cardiac plexus, all of which requires for the laryngeal nerve to be long enough.

Unless I found a good explaination for that, I think I’m going to remove this example from my counterapologetic arsenal 🙂

[…] evolutionary reasons for this many times; you can see the full explanation in WEIT or read about it here. This diagram shows how it worked: the nerve used to line up with a blood vessel, both servicing […]

From an engineering point of view, what changes would you make to the human body?…

“One of nature’s worst designs is shown by the recurrent laryngeal nerve of mammals. Running from the brain to the larynx, this nerve helps us speak and swallow. The curious thing is that it is much longer than it needs to be. Rather than taking a dir…

Jesse said,

“The jacket [of the book] depicts a chronological sequence of fossils showing the evolution of birds; we do not know whether the actual line of descent included the first three species, but the origin of modern birds almost certainly involved a sequence very much like this one”

If evolution is true, then why use such obscure and inconclusive samples from around the world as the representation of the truth of evolution? Phrases like “we do not know” and “almost certainly” are all too common from evolutionists. Couple that with big claims and accusations of those who interpret scientific data from the perspective that it looks and functions like something designed, and you get the blind, frustrated rants of evolutionists. Why not accept the obvious?

Craig said,

Whoever told you that the LRLN originates in the brain and only innervates the larnyx is an idiot. The LRLN, according to Gray’s Anatomy (40th Ed., 2008), arises (originates from) the Vagus nerve under the left aorta, and travels a straight line to the larnyx, innervating the esophagus and the trachea along the way, and also provides several cardiac filaments to the deep part of the cardiac plexus. The silly “LRLN” argument arises from the errant notion being peddled by some unscrupulous Atheists that the LRLN originates in the brain, and that it only innervates the larnyx. Get off the cookie-cuter Atheist websites that are ran by the ministers of misinformation, and get your nose in a medical book!

Anonymous said,

Very well. Now would you be so kind as to enlighten me, given your superior knowledge in human anatomy, why this nerve has to run all that distance (meters in giraffes) instead of branching off directly at the larynx, as it does in fish (innervating the gills)? Surely a direct route would have made more sense from a designer’s viewpoint, wouldn’t you say? Why does it have to be recurrent rather than direct?

How did the recurrent laryngeal nerve evolve from fish to human beings?

” the nerve used to line up with a blood vessel, both servicing the gills of our fishy ancestors. When the vessel moved backwards during evoution, the RLN was constrained to remain behind it, still retaining its connection to the larynx, which evolved…

Byron said,

Are there perhaps adaptive advantages in running the RLN down and back up? Coyne says it could be maladaptive (because the nerve is exposed to damage in places where it need not be). But could it also be adaptive? For example, perhaps there are common injuries in the space where a direct routing of the nerve would pass, and so God re-routed that thing down and around.

I dislike when scientists make patent conclusions about why something is so without hedging with “it appears that” or “our best guess is”.

Evolution *could* have directly routed the nerve if a mutation caused a direct routing (a big leap, yes, but aren’t there other big leaps in the fossil record?). That direct routing would be more adaptive and would be presumably preferred to this day, thereby robbing us of this lovely debate.

We clearly do not understand vast quantities of things about our bodies (especially our brains), so why can we conclude that this nerve is poorly designed? Isn’t that arrogant?

Byron said,

I don’t think a mutation could have caused a direct routing because that end organ did not exist at that time, where would it route to? Fish don’t have voice boxes. Instead that nerve was routing to the end organ it had at that time which was indeed posterior to the organ you talking about which makes pefect sense that it went all the way down.
Secondly making the nerve take a longer route through the body can only create more vulnerability for injury and it still needs to be routed to the same vicinity so how would that be avoiding common injury? I’m no expert but I’m just asking.